Fluorescent lamp circuit with regulation responsive to voltage, current, and phase of load

Abstract

In a fluorescent lamp, a "soft" start-up circuit initially applies a lamp, or inter-electrode, voltage which is limited to a peak voltage that will not start the lamp prior to heating of the lamp cathode to the proper temperature. The lamp cathode is then heated to the proper start-up temperature after which the lamp voltage is increased to a value well in excess of the ignition voltage required for all lamp types and operating characteristics in initiating lamp operation. The increased lamp voltage is applied in a pulsed manner until the lamp is ignited, whereupon the lamp may be operated at normal lamp current and cathode voltages or the lamp filaments may even be turned off with a consequent savings in input power.

I claim: 
     
       1. A start-up circuit energized by a direct voltage source for driving an inverter circuit coupled to a fluorescent lamp having a plurality of electrodes for initiating operation of the fluorescent lamp, wherein fluorescent lamp operation is sustained by application of a first voltage V 1  across the fluorescent lamp electrodes by the inverter circuit said start-up circuit comprising: power-up circuit means coupled to the direct voltage source for generating a power-up signal; drive signal control means coupled to the inverter circuit and to said power-up signal for providing first drive signals to the inverter circuit to provide a second substantially constant voltage V 2  to the fluorescent lamp electrodes for the heating thereof for a predetermined period of time; and pulse generating means coupled to said drive control means and to said power-up circuit means and responsive to said power-up signal for generating a high voltage start-up pulse following receipt of said power-up signal and for providing said start-up pulse to said drive signal control means, whereupon said drive signal control means provides second drive signals to the inverter circuit to provide a third voltage V 3  to the fluorescent lamp electrodes for initiating the operation of the fluorescent lamp, where V 3  >V 1  and where V 3  >V 2 . 
     
     
       2. The start-up circuit of claim 1 further comprising first feedback means coupling said power-up circuit means to the fluorescent lamp for providing a lamp voltage signal to said power-up circuit means and wherein said drive signal control means regulates the lamp voltage by controlling said first drive signals during fluorescent lamp start-up. 
     
     
       3. The start-up circuit of claim 2 further comprising second feedback means coupling the fluorescent lamp to said drive signal control means for providing a lamp current signal thereto and wherein said drive signal control means regulates the lamp current by controlling said first drive signals following fluorescent lamp start-up. 
     
     
       4. The start-up circuit of claim 1 wherein said pulse generating means includes timing means for delaying the providing of said second drive signals to the inverter circuit and thus the providing of the third voltage V 3  to the fluorescent lamp electrodes for a predetermined time period. 
     
     
       5. The start-up circuit of claim 4 wherein said timing means includes an RC network and said predetermined time period is established by an RC time constant thereof. 
     
     
       6. The start-up circuit of claim 1 wherein said predetermined time period is a minimum of 0.6 second. 
     
     
       7. The start-up circuit of claim 1 wherein said power-up circuit means includes enable signal generating means for generating and providing an enable signal to said drive signal control means following receipt by said power-up circuit of a direct voltage from the direct voltage source. 
     
     
       8. The start-up circuit of claim 7 wherein said enable signal generating means includes timing means for delaying the providing of said enable signal to said drive signal control means a predetermined time period following receipt by said power-up circuit of a direct voltage from the direct voltage source. 
     
     
       9. The start-up circuit of claim 8 wherein said timing means includes an RC network and said predetermined time period is established by an RC time constant of said network. 
     
     
       10. The start-up circuit of claim 1 wherein said drive signal control means includes a feedback control network for regulating drive signals provided to the inverter circuit and the fluorescent lamp current following fluorescent lamp start-up. 
     
     
       11. An electronic circuit for initiating and sustaining operation of a fluorescent lamp having a plurality of electrodes from a source of electrical power having a voltage amplitude varying in time, wherein fluorescent lamp operation is initiated by application of a first voltage V 1  across the fluorescent lamp electrodes, comprising: inverter circuit means receiving power from said source and including first and second controlled switches gated to conduction respectively in alternate cycles of inverter frequency for generating a high frequency electrical signal for supplying power to the fluorescent lamp; sensing circuit means for generating a control signal representative of lamp current; feedback control circuit means for controlling the gating of said controlled switches in response to said control signal for regulating lamp current to a predetermined value in sustaining fluorescent lamp operation; power-up circuit means energized by said source for providing a second voltage substantially constant voltage V 2  to the fluorescent lamp via said feedback control circuit and said inverter circuit means prior to the operation of the fluorescent lamp for heating the electrodes of the fluorescent lamp to an operating temperature; and pulse generating means coupled to said feedback control circuit means and to said power-up circuit means for providing a third voltage V 3  via said feedback control circuit means and said inverter circuit means to the fluorescent lamp for initiating operation of the fluorescent lamp following a predetermined time interval after receipt of said second voltage V 2  by said feedback control circuit means, where V 3  >V 1  and where V 3  >V 2 . 
     
     
       12. A start-up circuit energized by a direct voltage source for driving an inverter circuit coupled to a fluorescent lamp having a plurality of electrodes for initiating operation of the fluorescent lamp, wherein fluorescent lamp operation is sustained by application of a first voltage V 1  across the fluorescent lamp electrodes by the inverter circuit, said start-up circuit comprising: power-up circuit means coupled to the direct voltage source for generating a power-up signal; drive signal control means coupled to the inverter circuit and to said power-up signal for providing first drive signals to the inverter circuit to provide a second substantially constant voltage V 2  to the fluorescent lamp electrodes for the heating thereof for a predetermined time period; and pulse generating means coupled to said drive signal control means and to said power-up circuit means and responsive to said power-up signal for generating a high voltage start-up pulse following receipt of said power-up signal and for providing said start-up pulse to said drive signal control means, whereupon said drive signal control means provides second drive signals to the inverter circuit to provide a third substantially constant voltage V 3  to the fluorescent lamp electrodes for initiating the operation of the fluorescent lamp, where V 3  >V 1 .